His "horn" is actually the operational end of his portal device. Do not look directly into it! The thing at the end of his tail is a highly adaptive data port. He can use it to jack into, and interface with, nearly any computer system in existence. Strangely, he has an odd preference for antique video game consoles. (He's damn near unstoppable at Street Fighter.) His tail can also function as a hand of sorts, which he can use to pick up and manipulate small objects.

The Professor's cutie mark is a secret known only to The Professor himself, Odyssey, and the masked mare who calls herself Eliza. (In other words, you tell me lol.) I'd wager it's something time-related, however. Same with Liz.

As for Odyssey, that's a good question... I never really thought about it. I based his design here more on a real horse, as you can see. I'm not sure what his cutie mark would be if he were an FiM-style cybercorn... What do you think?